Hydrological modeling and water allocation in the Piranhas-Açu River Basin in the eastern axis of the São Francisco River integration project

This study presents the integrated application of the lumped hydrological model SMAP and the optimization library Pywr to assess water allocation in the Piancó-Piranhas-Açu river basin, located in the Brazilian semi-arid region. We developed comparative scenarios with and without inflows from the São Francisco River Integration Project (PISF), based on historical monthly series of rainfall and streamflow, combined with sectoral demands obtained from the National Water Use Register. Results showed that the PISF inflow, which began in December 2021, improved flow regularity, reduced the frequency of critical storage levels in the reservoirs, and increased the reliability of demand supply. Public water supply was the most benefited sector, with a significant reduction in deficits and higher frequency of full demand satisfaction, while irrigation showed modest improvements due to the legal priority of human consumption. These findings underscore the strategic importance of the PISF in strengthening regional water security and demonstrate the potential of integrated modeling as a decision-support tool, providing technical evidence for water management policies in critical semi-arid basins. Keywords: PISF, semi-arid, water allocation.